Abstract:Tropical Yunnan is the tropical border area of SE, S & SW Yunnan. This area is the range of tropical rain forests and tropical monsoon forests in Yunnan province now. Its seed plants flora has 4915 species in 1447 genera and 248 families. It is basically tropical in nature but has some obvious transitional characteristics from tropical to subtropical floras, so that it is best to be said as a north variant of tropical flora. After analysing its floristic elements, the eastern part and western part of tropical Yunnan have many differences in the geographical relationship, vicariance, endemism, as well as floristic origin and differentiation. The cause of these differences may be due to their different geological backgrounds. So that it is reasonable to divide these two parts of tropical Yunnan into different regions of palaeotropical kingdom, but the range and boundary of these two floristic regions should be based on the map of idealized vegetation of Yunnan (Wu & Chu, 1987).